Structure for controlling the output voltage of a transformer



Nov. 5, 1957 G. H. ALLEN 2,812,478 STRUCTURE FOR CONTROLLING THE OUTPUT VOLTAGE OF A TRANSFORMER 7 Filed April 26, 1956 2 Sheets-Sheet 1 INVENTOR. 652/742 19. HZLE/V 4g. 4 zz/dfiwgm iw H TTOHNE YJ' Nov. 5, 1957 2,812,478

G. H ALLEN STRUCTURE FOR CONTROLLING THE OUTPUT Filed April 26, 1956 VOLTAGE OF A TRANSFORMER v 2}Sheets-Sheet 2 INVENTOR. 65mm H. flux/v u/m Maya k HTTORNEYS Unite States Patent 0 STRUCTURE FOR CONTROLLING THE OUTPUT VOLTAGE OF A TRANSFORMER Gerald H. Allen, Kalamazoo Township, Kalamazoo County, Mich, assignor to Allen Electric and Equip" ment Company, Kalamazoo, Mich, a corporation of Michigan Application April 26, 1956, Serial No. 580,792 9 Claims. (Cl. 317-157.6)

This invention relates to transformer structure and particularly to an adjustable voltage transformer of the type adaptable for manufacture at low cost and in small sizes for use in shops and in automotive service stations, especially for such use as in connection with battery charging units.

Transformers of this general type and including a primary and a secondary winding, have previously been provided with a slider acting against the exposed wires of the secondary winding for the purpose of determining the number of turns of such winding which are incorporated into the output circuit of the transformer. Further, it has previously been recognized that the slider should be permitted to contact only one secondary wire or turn at a time, for where the slider contacts more than one such wire, there is a short circuit provided from one such wire to the next adjacent wire resulting in arcing and burning of both the wires and of the slider contacts. Previous attempts to meet this problem have, insofar as I am aware, involved relatively complex and/ or delicate structures, including the use of high resistance contacts to minimize short-circuiting current between adjacent wires. These structures have either been too expensive to be practical or have not stood up well in use, or both.

Also, it has been recognized in the past that it is desirable to provide some kind of yieldable stop mechanism, as a detent mechanism, for tending to hold the contact of the slider in position against a given wire and to resist its stopping in a position where it contacts more than one wire at a time or in a position where it will not contact any wire. Previous attempts in this direction have, insofar as I am aware, utilized the irregularity of the wire itself to provide the detent structure, but this has not been desirable due to its lack of flexibility in any given case and due to the relatively ineffective detent operation provided by wire of small size.

Further, even where such detent operation was acceptable and where the contact of the slider could be properly arranged to contact only one Wire at a time, there has still been a tendency for arcing as the contact was drawn away from each individual wire. This tended to pit the contact, which in turn would diminish the effectiveness of its electrical conductivity with respect to a wire against which it was in contact, and in general tend to provide an unsatisfactory device. It has thus been desirable to provide a switch in such association with the slider that a circuit could be opened whenever the slider contact was in other than full contact with one, and only one, of the wires of the secondary winding. A switch can be made with contacts better able to resist or avoid such arcing, than can the slider contact, as by use of molybdenum, or molybdenum alloy, or other non-arcing material, or the switch contacts can be replaced with less effort or expense than would be required to replace the slider contacts or the wire of the secondary winding. Thus, in the event that the arcing is not successfully resisted, use of such a switch will provide a more effective and sturdy Til device than one wherein such arcing is permitted to occur between the slider and the secondary wires.

It is further desirable to provide transformer structure of the general nature aforesaid which will be of rugged construction so that the original calibration for indication of voltage output will remain accurate throughout the normal life of the transformer and will not be disturbed even though the transformer is subjected to the rough usage often encountered in garage and service station operations.

Accordingly, a principal object of the invention has been to provide an adjustable voltage transformer which will be capable of easy and accurate adjustment and which, when so adjusted, will remain through a long period of useful life in such adjusted position under all normal conditions of use.

A further object of the invention has been to provide a transformer, as aforesaid, in which the selection of the voltage may be made by convenient, manually controllable means, and wherein such means may be used to indicate accurately the value of the voltage being selected.

A further object of the invention has been to provide a transformer, as aforesaid, having a sliding member for selectively contacting the turns of the secondary winding arranged so that such sliding member cannot contact more than one turn at a time of said secondary winding.

A further object of'the invention has been to provide a transformer, as aforesaid, in which arcing between said sliding member and the turns of the secondary winding will be held to a minimum.

A further object of the invention has been to provide a transformer, as aforesaid, of simplified structure where in the structure insuring accurate voltage selection is also the structure which insures the ruggedness of the transformer and its ability to maintain its original calibration accurately in spite of rough usage involving substantial and frequent physical shocks and impacts.

A further object of the invention has been to provide a transformer, as aforesaid, utilizing a switch for automatically opening the input circuit during the travel of the slider contact from one turn to the next of the secondary winding and thereby providing further protection against the possibility of short-circuiting between adjacent secondary turns by the slider contact.

A further object of the invention has been to provide a transformer, as aforesaid, which will be economical to manufacture, which will be sturdy and reliable through a long period of use and which will be capable of withstanding rough usage.

Other objects and purposes of the invention will be apparent to persons acquainted with apparatus of this general type upon reading the following specification and inspecting the accompanying drawings, in which:

Figure l is an oblique view of a transformer construction characterizing the invention.

Figure 2 is an end elevation of said transformer.

Figure 3 is a sectional view taken along the line IIIIII of Figure 2.

Figure 4 is a diagrammatic view of the transformer circuit and output selector mechanism.

Figure 5 illustrates an alternative arrangement for the cam wheel.

Construction in general In meeting the objects and purposes above set forth, I have taken advantage of the fact that transformers, at least of the type intended for use with battery chargers and other similar garage and service station apparatus, do not normally require voltage output regulation through the full range from zero to the maximum voltage output. Normally, such regulation is required from, and starts at,

a point substantially above zero and then extends up through maximum output. Therefore, I am ableto shorten the length of the transformer (Figure 1) materially by providing a single primary winding 11 wound in the usual manner on the core or frame 12, and a secondary winding wound in two layers or sections 13 and 14, which are concentric with each other and with the primary winding.

A first orinner section 13 of said secondary winding is immediately outside of, and surrounding, the primary winding 11 and the second or outer section 14 of said secondary winding is immediately outside of, and surrounding, the first section of the secondarywinding; Only the second section of the secondary winding is ac-. cessibleto, and engageable by, the contacts 15 of a voltage selecting slider 16. A.comb-shapedstructure'17 is placed between the first and second sections of the secondary winding beneath thepath of said slider. The teeth 13 of said combextend outwardly between theturns 1-3 of the second section of the secondary winding for positively positioning said turns at'all times, even if the transformer is subjected to rough usage. The comb is, of course, of non-conductive material and its teeth effectively separate the turns of the second section of the secondary winding sufficiently to insure that the slider contacts only one of said outer turns 19 at a time.

Said slider 16 is carried by a rotatable screw 21 which in turn maybe manually rotated by a convenient carn wheel 22. The peripheral contour of said wheel is made irregular, or cammed, and includes a detent portion 23. A spring loaded cam follower 24 rides'on the cammed periphery 25 of said cam wheel and tends to oppose movement of said camwheel in either rotative direction when said cam follower encounters said detent portion. Said detent portion is so'arranged with respect to the lead of the screw 21 and the position of the slider thereon that, at the points where the cam follower tends tooppose rotative movement of the cam wheel, the slider is in proper contact with one turn of the second section 14 of the secondary winding. Thus, said cam wheel and follower will tend to hold said slider in contact with a selected turn of the outer section ofthe secondary Winding until an operator deliberately effects rotation of the cam wheel and thereby effects movement of the slider to another turn of said outer section of the secondary winding.

A- switch 26, also preferably actuable by saidcamfollower,.is provided in the primary circuit-and is arranged to be in closed position onlywhen said cam follower engagesthe detent portion-of the cam wheel. Thus, the

transformer will" be energized onlywhen the contacts of the slider are in proper contact-with-a selected single turn ofthe outer section of the secondary winding and, therefore, only when the cam follower is indetent position and the switch-26'is closed. Said switch will be opened prior to the time that said slider contacts 15 are disengaged from the particular turn 19 of the outer section of the secondary Winding with which. they have been engaged.

'Details 0 construction The frame 12 of the transformer may be of conventional, laminate construction having a pair of spaced openings 3t) therethrough, which are substantially perpendicular to the planes defined by the individual laminates of said frame 12 in a. conventional manner. The primary winding 11 is wrapped around, and insulated from, the core portion 31 ofthe frame 12 disposed between the openings 39. The inner secondary winding 13 is wrapped around the primary winding 11 in a substantially concentric position and insulated therefrom. The support plate 32 of the comb structure 17- is disposed upon the outside of the. inner secondary winding 13 substantially parallel with the elongated core portion 31 of the frame 12. A comb-shaped insulator 33, having uniformly spaced. teeth, 18 with parallel grooves '34 disposed between said teeth, is mounted upon the support plate 32 remote from the inner section of the'secondary winding 13 and extends lengthwise of the support plate 32 with the grooves running transversely of said support plate and parallel with said turns. The second, or outer, section of the secondary winding is arranged around, and concentric with, the first section thereof, and outside of said comb structure.

A selected number, here one, of turns 19 of the outer section of the secondary winding 14 are disposed within each groove 34. The inner and outer sections of the secondary winding are electrically connected with each other (Figure 4). They are also substantially concentric with each other as well as with the primary winding 11. That portion of each of the turns 19 of the outer section 14 of the secondary winding, which is disposed within one of the grooves 34, is un-insulated on at least its radially outer surface for reasons appearing hereinafter.

A pair of flanges 35. and as (Figures 1 and 3) extend in the same direction from the opposite ends of: the support plate 32', which direction is upwardly from the core 12 in this embodiment. The screw 21 is rotatably supported near its opposite ends upon the flanges 35 and 36 in a conventional manner. Lock collars 37 prevent accidental disengagement of the screw 21 from said flanges 35 and'36. The slider 16' is mounted upon the screw 21 for movement axially thereof upon rotation of said screw. In'this embodiment, the slider moves the distance between the centerlines of two. adjacent grooves 34 with each rotation of said screw. However, this may be varied as desired. There are any desired number, two in this embodiment, of contacts 15 on the slider 16, which are fabricated from resilient, conductive material and may be substantially identical in. shape and size. They are so arranged that they will continually press against the upper surface of the insulator 33 or the. turn 19 of the outer section 14 of the secondary winding disposedwithin the adjacent groove 34.

The cam wheel 2'2 is secured to. one end of the'screw 21 for effecting rotation of the screw 21, hence movement of the slider 16 axially of said screw 21. The detent portion 23 of said wheel 22 may be a recess in the periphery 25 of said wheel, as shown in Figure 2. The cam follower 24 is pivotally mounted upon one end of an arm 38, the other end of which is pivotally mounted upon a bracket 39 which issecured upon the upper surface of the core 12. The pivot arm 38 is urged upwardly, thereby causing the cam follower 24 to bear snugly against the periphery25 of the Wheel'22, by means such as the spring, 41' extending between said pivot arm 38 and the bracket 39. The switch 26 may be of any conventional type, such as a rotary switch mounted upon the bracket 33; which is connected to, and operable by, the pivot axle 42of'the pivot arm 38'. A further irregularity, as a detent recess 46, of depth insufficient to close the switch 26, may be provided; if desired, in the wheel 22 for purposes asappearing below.

Operation The operation. of the apparatus has been generally indicated above: in connection with the description of its structure. However, the. operation will be' summarized for purposes of clarity and completeness of disclosure.

Alternating current supplied through the primary winding. of the transformer will, in the usual manner, induce voltage in thesecondary. winding proportional to the number ofv turns provided therein and the voltage. of theoutput may be selected by varying; the number of turns of the secondary winding between the terminal connected to the inner section of the secondary winding and the turn contacted by the slider contact 15. Rotation, which rotation'will be manual in the embodiment here utilized to illustrate the invention, of'the cam wheel 22' will rotate the screw 21 and therebyradjust the position of the slider 16 withrespect to the turnsoffthe second section ofthe. secondary winding and effect. such. selection:

The relationship between the cam follower 24 and the detent portion 23 of the cam wheel will, when said cam follower enters said detent portion, tend to hold said cam wheel against further rotation. Thus, by so arranging the parts that said cam follower is in the detent portion of the cam wheel at such a time that the contact 15 bears against one and only one of the turns of the secondary winding, the apparatus will tend to stop, and remain until expressly moved, in a position where the contact 15 contacts one, out only one, of the turns of the secondary winding.

By spacing the turns of the second section of the secondary winding far enough apart that the contact 15 can touch only one of them at a time, provision is made against shorting through said contact between adjacent turns of the secondary winding. Simultaneously, by forming the secondary Winding in two layers, such spacing of the desired portion of the secondary winding is made possible without unduly lengthening the overall construction.

The switch 26, if used, is closed (Figures 1 and 4) and the transformer thereby energized only when the cam follower 24 is in the detent portion or recess 23 of the wheel 22. Also, any material dislocation of the cam follower 24 from said recess will open the switch 26. The contacts 15 are aranged so that the free ends thereof adjacent the comb-shaped insulator 33 will be simultaneously disposed directly above the center line of a groove 34 in said insulator and, therefore, engageable with a turn 19 within said groove when the cam follower 24 is within said recess 23. Said free ends of said contacts 15 will move from such position with respect to one groove 34 to a similar position with respect to the next adjacent groove in either direction upon the rotation of the wheel 22 through 360.

It will be observed that the slider 16 will move a relatively short distance axially of the screw 21 by comparison with the circumferential distance moved by the recess 23 with each rotation of the wheel 22. Since the amount of rotation of Wheel 22 necessary to effect a dislocation of the cam follower 24 from the recess 23, hence an opening of the switch 26, will be relatively small, the accompanying movement of the slider 16 will be practically negligible. Accordingly, the switch 26 will be opened, thereby deenergizing the primary circuit, before the contacts 15 can move any appreciable distance lengthwise of the insulator 33 and, particularly, before they can be moved away from their position of full contact with the turn 19 with which they are engaged. As a result of this arrangement, the terminals of the switch 26 take most of the wear resulting from breaking the circuit of the secondary each time the slider 16 is moved from one turn to the next adjacent turn.

The switch 26 makes it possible to reduce the distance between adjacent turns 19 to a minimum required for insulation purposes, since the switch 26 is opened by the cam follower 24 well before the contacts 15 come to a position where they will separate from any one turn, with which they are engaged.

While the foregoing construction has assumed that the adjustability of the apparatus will be confined to the upper range of the possible voltages obtainable from the full secondary winding, it will, of course, be recognized that by providing suitable switches and a suitable conductor for cutting out the first section of the secondary winding, the transformer can be readily converted by the operator into a fully adjustable, lower voltage, transformer. Where the detent recess 46 is used, this will help the operator to locate the off position and will tend to hold the charger in such position until positively moved. However, it is not deep enough to close the switch 26.

A suitable indicator, as a pointer 50, may be placed on the slider 16 and caused to cooperate with a scale 51 placed on a surrounding casing 52. This will provide 6' a direct and accurate indication of the voltage output of the transformer for a given voltage input.

It will also be recognized that the specific arrangement of cam shape and of cam follower may be varied widely with known mechanical apparatus without altering the ultimate operation of the device as described. Figure 5 illustrates one alternate structure with numerals applied corresponding to numerals in Figures 1 to 4, plus the suflix a.

Although a particular, preferred embodiment of the invention has been disclosed hereinabove for illustrative purposes, it will be understood that variations thereof, which lie within the scope of such disclosure, are fully contemplated unless specifically stated to the contrary in the appended claims.

I claim:

l. in an adjustable voltage transformer, the combination comprising: primary and secondary windings in inductive relationship to each other; at least part of the turns of said secondary winding being externally accessible and axially spaced from each other; a slider including a contact and means effecting controllable movement of said slider axially of said secondary winding and adjacent thereto in such manner that said contact may successively contact the turns of said secondary winding; 9. pair of output terminals and means connecting said contact to one of said terminals and means connecting one end of said secondary winding to the other of said terminals; manually rotatable means for effecting movement of said slider axially of said secondary winding, said means including a cam having a low point thereon and a spring loaded cam follower following said cam and resiliently resisting movement out of the low point of said cam; said cam follower, the low point of said cam, said rotative means, said slider and the contact carrier thereby, and the external turns of said secondary Winding all being mutually related with respect to each other in such a manner that said contact will be in contact with one of said turns when and only when said cam follower is substantially in said low point.

2. The device defined in claim 1 wherein said contact is in engagement with successive ones of said turns each time said cam follower enters the low point of said cam.

3. The device defined in claim 1 including a switch actuated by said cam follower and connected in series with one of said windings, and arranged to open the circuit of such winding whenever said contact is in a position other than in substantial contact with one, but only one, of said turns.

4. An adjustable voltage transformer, comprising: a core; primary and secondary windings on said core in inductive relationship, part of the turns of said secondary winding being exposed and spaced from each other; a conductor successively engageable with said exposed turns, at least part of such engagement being made with not more than one said turn at a time; control means for moving said conductor transversely of said turns; disconnect means breaking the electrical circuit of one of said windings before said conductor leaves contact with any one turn and restoring said circuit after it engages the next successive turn; and detent means resiliently urging said conductor to remain in engagement with not more than one turn at a time.

5. The structure of claim 4 wherein said disconnect means includes an electrical switch in series with said primary winding and a switch actuator responsive to the operation of said detent means, said switch being closed only when said conductor is engaging one turn, but not more than one turn.

6. In an adjustable voltage transformer, the combination comprising: a frame; primary and secondary windings mounted on said frame in inductive relationship to each other, said secondary winding being composed of two sections, the first section being concentric with, and

radially outward of, the primary winding and the second section being concentric with, and radially outward of, said first section; a comb member of insulative material positioned between the first and second sections of said secondary winding, the respective turns of said second section lying between the teeth of said comb for positive placement and rigid holding thereof with respect to said frame; a slider, including a contact, and means effecting controllable movement of said slider axially of said secondary winding in such a manner that said contact successively engages the turns of said second section of said secondary winding; means for effecting such axial movement of said slider; and detent means for selectively holding said contact in engagement with a selected one of the turns of said second section of said secondary winding.

7. An adjustable voltage transformer, comprising; a core; primary and secondary windings on said core in inductive relationship, apart of the turns of said secondary winding being exposed and spaced from each other; a slider including a contact and means effecting controllable movement of said slider along the exposed turns of said secondary winding so that said contact may successively contact said exposed turns; a disconnect switch in series with said primary winding for breaking the electrical circuit of said primary winding, said switch being closed *8 when said contact is engaging only one of said exposed turns; and means for selectively holding said contact in engagement with a selected one of said exposed turns.

8. A transformer as set forth in claim 7 wherein said slider is mounted for axial movement along said exposed turns; means for moving said slider axially; and an actuator operated by said last named means for actuating said switch so that said switch is' opened when said contact is in a position between adjacent exposed turns.

9. A transformer as set forth in claim 8 wherein said means for moving said slider includes a rotatable cam having a low point thereon; a spring loaded cam follower following said cam and resiliently resisting movement of said cam when said cam follower is in the low point of said cam; said cam follower actuating said switch to open same when said cam follower moves out of the low point of said cam.

References Cited in the file of this patent UNITED STATES PATENTS 

